In a conventional mechanical seal, a sliding surface in the form of a seal ring, which contacts and slides on a mating material to seal a fluid, is normally of a flat shape. And, this surface is a so-called mirror surface in which pores and the like do not exist (at least, not by design).
This type of mechanical seal has various combinations of members. The mechanical seal for use in a service with a large PV value (where P is the pressure of the sealed fluid and V is the peripheral velocity) is mostly selected from the combinations of cemented carbide/carbon, and cemented carbide/cemented carbide.
However, in a freezer and the like, in addition to requiring a high PV value, a large thermal shock is experienced because of the repetition of running and stopping, and there are problems such that heat cracks are produced in the sliding surface, and that with carbon material, bulges known as blisters are produced.
Many different proposals have been presented to increase the lubricating ability of the sliding surface, in order to eliminate this type of problem.
One such proposal presents a design in which the shape of the seal ring is modified to increase the lubricating ability. For example, there is provided an end-face lubricating seal (hydrostatic seal) in which a plurality of through holes are provided between the sliding surface and the opposite surface, and a lubricating fluid is fed by a pump from the holes in the opposite surface to the sliding surface; or, there is a hydrodynamic seal provided with a channel or a notch extending from the fluid side into the sliding surface close to its center, which conducts a sealed fluid, which plays the role of a lubricant during operation, to the sliding section by means of a wedge effect based on the viscosity of the fluid; or, there is a thermohydrodynamic seal, or the like. These can be used at a higher PV value than conventional seals to reduce the coefficient of friction.
However, with this type of hydrostatic seal, hydrodynamic seal, or thermohydrodynamic seal and the like, in order to bring about that effect, a complicated process must be performed on a cemented carbide, and, in considering the difficulty in processing the cemented carbide, the processing time is exceedingly long in comparison with the conventional seal. Furthermore, there is the drawback that when the shape of the cemented carbide is complicated, stress concentration is readily produced and breakage can easily occur. Accordingly, this type of seal can only be used in limited applications at the present time. Therefore, a new material is required for which this type of processing is unnecessary.
In a sliding surface which must answer to this sort of demand, a mechanical seal with high lubricating characteristics at the sliding surface has been proposed in which after a lapping process, or shot blast process, or etching process is performed, a polishing process is applied to the sliding surface, so that a plurality of minute holes are formed. However, in the case of this type of structure, because the holes are very small and only formed at the sliding surface, the holes disappear as the sliding surface is subjected to wear, so there is the drawback that the improved lubrication result cannot be maintained for a long period of time.
In addition, a mechanical seal has been proposed in which the seal ring itself formed with a porous material. In this case, the strength of the seal ring is reduced, so that a high PV value cannot be obtained, and in addition, another problem occurs wherein the leakage from the holes cannot be ignored if the magnitude and volume of the holes are significantly large.